1. Field of the Invention
The present invention relates to a conductive paste, especially a conductive paste suitable for forming a terminal electrode of a laminated ceramic electronic component, for example, a monolithic ceramic capacitor and a laminated positive temperature coefficient thermistor. The present invention also relates to a method for manufacturing a laminated ceramic electronic component using the conductive paste and the resulting laminated ceramic electronic component.
2. Description of the Related Art
Hitherto, Ag, Ag—Pd, etc., have been used as a material for an internal electrode of a monolithic ceramic capacitor, which is one of laminated ceramic electronic components. However, these internal electrode materials are expensive and, therefore, a base metal, Ni, which is a less expensive material has come into use. On the other hand, Ag having excellent conductivity and capable of being baked at a low temperature has been used as a terminal electrode material of the monolithic ceramic capacitor. For example, a Ni layer has been formed on this terminal electrode made of Ag, and a solder layer or a Sn layer has been further formed in order to enhance soldering and, thereby the monolithic ceramic capacitor has been produced.
As an internal electrode material for a laminated positive temperature coefficient thermistor, one of laminated ceramic electronic components, Ni in ohmic contact with ceramic has been used as an n-type impurity semiconductor. Laminated ceramic green sheets and internal electrodes have been fired simultaneously under a reducing atmosphere. Subsequently, terminal electrodes have been baked in the atmosphere while the ceramic itself has been oxidized again and, therefore, the laminated positive temperature coefficient thermistor having a desired positive temperature coefficient of resistance has been produced.
Ni and Ag do not form a solid solution with each other. Consequently, when Ni is used as the internal electrode of the monolithic ceramic capacitor and Ag is used as the terminal electrode, it is difficult to join the internal electrode and the terminal electrode and, therefore, there is a problem in that a desired capacitance cannot be achieved.
Cu, which makes a solid solution with Ni at any ratio, has been noted as the terminal electrode. However, it is necessary to conduct the baking under a reducing atmosphere when the terminal electrode is formed by baking a Cu-containing paste since Cu is likely to be oxidized and, therefore, an increase in the manufacturing cost is realized. Furthermore, since the oxygen concentration is low in the reducing atmosphere, the decomposition rate of the vehicle in the conductive paste is reduced, and there is a problem in that the carbon residue may affect characteristics.
Likewise, when Ag capable of being baked in the atmosphere is used as the terminal electrode material in the case of the laminated positive temperature coefficient thermistor, no mutual solid solution with Ni of the internal electrode is brought about and, therefore, joining is unlikely to occur. Examples of other terminal electrode pastes capable of being baked in the atmosphere include an Al paste and a Zn paste. However, baking electrodes of these Al and Zn pastes have poor solderability and, in addition, there is a problem in that when electrolytic plating is attempted thereon, the Al or Zn electrode itself elutes into an electrolytic solution.